State the principle of moving coil galvanometer?

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Hint: Before starting our discussion about the principle of moving coil galvanometer it is important to understand what the galvanometer is. Generally, Galvanometer is an instrument that is used to check the presence of an electric field in an electric circuit.

Complete step by step solution
A moving coil galvanometer is a type of precision galvanometer that consists of a coil that is placed between two permanent magnets and the coil is suspended freely so that it can move easily even for a very small amount of current. A small mirror is attached to the coil so that it will show deflection on a scale that can be placed in front of it. When it is connected in a series connection in the electric circuits and when the current flows through the coil it shows deflection because the current is directly proportional to the magnetic field.
Hence the principle on which a moving coil galvanometer works can be stated as to when a current-carrying coil which is suspended freely in a magnetic field a torque acts upon the coil and due to this torque the coil rotates and the deflection of the coil is directly proportional to the current flowing through the coil.

There are many advantages of the moving coil galvanometer in comparison to a simple galvanometer. Their scales are in uniform arrangements. They can be used even for the very small amount of current that cannot be detected by a simple galvanometer. They are very reliable and are very accurate. They are not easily affected by strong magnetic fields.